The Milwaukee Health Department doesn't collect water samples at its three beaches on Wednesdays, so Thursday's closure is based on Tuesday's water sample, which showed more than 2,419 per 100 milliliters of water at a temperature of 77 degrees.

Despite the warning, more than 20 people were swimming at the beach at noon Wednesday as the region faced its warmest temperatures of the year. Milwaukee County Executive Chris Abele reminded residents at a news conference Wednesday afternoon to pay attention to posted signs at beaches to make sure that swimming in the water was safe.

Sarah DeRoo, spokeswoman for the City's Health Department, said heat as well as stagnant water could be associated with the high bacteria levels in Tuesday's sample.